Positive skin tests to fern spore extracts in atopic patients.

Thirty-six atopic and eight non-atopic adult volunteers who had been exposed to ferns in their homes, were skin tested with extracts obtained from seven species of house ferns. Out of the 36 atopic patients, 18 had positive skin reactions to at least one out of seven species of the most common house ferns, whereas none of the non-atopic, healthy controls had positive reactions to any of the ferns.